The (Petri) Dish: Trouble with mosquitos

<b>ThinkStock</b>Insecticide-soaked netting can help prevent mosquito bites, although the insects are becoming resistant to some of those chemicals, leaving researchers looking for some more sophisticated ways of combating malaria-transmitting mosquitoes.

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One of the many benefits of living in Colorado is the relatively low number of biting insects. Mosquitos, of course, do plague us most of the summer. Although mosquitos can carry West Nile virus, they otherwise pose little threat to most of the state's residents.

For many parts of the world, however, they are carriers of one of the world's most devastating diseases - malaria. More than one million people per year die of this awful disease, and its incidence is on the rise. We think of malaria as being limited to tropical countries, so it may surprise you to know the disease used to be endemic in much of Europe and North America and was only finally controlled in the early 1950s. The elimination of malaria depends on controlling the mosquitoes that transmit the disease. And herein lies a tale of intrigue that is a modern example of bio-warfare.

Malaria was a major public health problem in southern Italy in the 19th century, with almost half the country's population at risk of infection. Tragically, the life expectancy of Italians who worked on the land was less than 25 years. The solution to this problem came with the discovery by the Italian naturalist Giovanni Battista Grassi that malaria was transmitted by mosquitoes. The realization that malaria could be eradicated by controlling mosquitoes led the Italian government to initiate a program of mosquito management using insecticides and by draining the marshes where mosquitoes breed. Some of the most dramatic effects were seen in the Pontine Marshes near Rome, where Mussolini's troops dug drainage trenches and installed pumps that allowed fresh water to replace salt water and irrigate the land. This not only made the land suitable for agriculture but also suppressed the local malaria-transmitting mosquito population that thrived on brackish water. The incidence of malaria in southern Italy fell dramatically.

This would have been a wonderful story, but for Mussolini's alliance with Adolf Hitler during the early stages of the Second World War. This alliance was initially very strong. But by 1943, the Axis powers were in retreat, prompting Italy to change sides and join Britain and the United States in the fight against the Nazi regime. Driven by a sense of vengeance and a need to slow the Allies' northward advance in Italy, the Nazis reversed the pumps and specifically redirected water flow in the Pontine Marshes to allow salt water to once again flow freely. Masterminded by the German scientist and Nazi sympathizer Erich Martini, this allowed the malaria-transmitting mosquito population to rebound and reestablish malaria in the region. Just to make sure the job was complete, the Nazis destroyed the small boats used for spraying insecticides in the marshes and moved supplies of quinine (an anti-malarial drug) to Germany. The plan was effective: Incidence of malaria in that region of Italy rose from 614 in 1939 to 55,000 in 1944. This is a clear example of bio-warfare that contravened the Geneva Convention (of which Germany was a signatory at the time). According to Yale University historian Frank Snowden, it was "the only known example of biological warfare in 20th-century Europe."

A lesson to be learned from this story is that the incidence of malaria can be reduced by controlling the insect vectors that transmit the disease. Unfortunately, in Africa it is difficult to control malaria-carrying mosquitoes due to the geographical and political complexities of the region. The use of insecticide-saturated netting for sleeping areas has proved to be a relatively cheap and practical approach to the problem. But mosquitoes are becoming resistant to common insecticides, so more resilient approaches are needed. Today, scientists are working on fascinating new strategies to combat malaria-transmitting mosquitoes. One promising approach is the introduction of genetically altered mosquitoes that are unable to harbor and transmit the malaria parasite. The idea is that these mosquitoes will breed with the indigenous population and thereby block transmission of the disease.

In a future article, I will explore other changes mosquito populations may be undergoing worldwide, including the possible impact of climate change. In the meantime, the next time you bat away a mosquito on a mountain trek, just spare a thought for the folk that live in malaria-endemic regions.

David L. "Woody" Woodland, Ph.D. is the Chief Scientific Officer of Silverthorne-based Keystone Symposia on Molecular and Cellular Biology, a nonprofit dedicated to accelerating life science discovery by convening internationally renowned research conferences in Summit County and worldwide. Woody can be reached at (970) 262-1230 ext. 131 or woody@keystonesymposia.org.